Re: MI and anonymous unions

[Vladimir Prus <vladimir@codesourcery.com>]

On Wednesday 15 November 2006 20:20, Jim Ingham wrote:
> Support for anonymous unions & structures is another of the "things we
> fixed but haven't submitted back"...  We do pretty much what Vladimir
> suggests, though I use #anon#N for the varobj name: the choice doesn't
> much matter.  We still return a blank expression (since that's really
> what the  There's one other tricky bit 'caused by the fact that you
> might have more than one anonymous union or structure inside a
> structure.  This wouldn't be a problem, but the varobj code tends to
> look up structure elements by name, which obviously won't work here.
> So you have to convert all the code that looks up structure elements
> to use the index rather than the name.

Ah, I see. So this is not as easy change as I though.

> Another of the things we do in our varobj code for C++ is that we look
> up the dynamic type of objects (the same mechanism that "set print
> object on" uses, and the value & children we return are based on the
> dynamic type.  As soon as you do that, you really do need a "give me
> the expression that can recreate this varobj" for child varobj's.
> Otherwise the MI client needs to get all these dynamic casts right to
> get down to the proper child, which is a bit of a pain.

Good point.

> But it's a generally useful command.  We called it "var-info-path-
> expression" and given a varobj, it returns the expression that if
> evaluated would result in the same value.  Xcode uses this for "show
> in separate window" actions in the debugger variable view.  You can
> also use the to eliminate the "." for the anonymous structures or
> unions - though of course the MI client could do this too...

In fact, I've posted a patch that ports -var-info-path-expression to mainline 
some time ago and we talked briefly with Daniel some time ago.

I'll see if I can revive that patch.

Thanks,
Volodya